This invention relates in general to a switch for controlling the electric power supplied to a motor, for instance, an electric motor of a hand-operated power tool, and more particularly to a compact electronic switch comprising SCR or TRIAC and a trigger-type operating member for controlling the speed of a motor.
As can be seen, a conventional electrically operated switch would start a motor to its maximum speed immediately after being actuated, and cause severe vibration, especially, in the case of an electrically powered hand-type tools. If the objects handled with the motor are of high hardness, such as that in a lathe or drill mechanism, an accident may happen during operation even if the operator grasps it firmly. Furthermore, such severe vibration resulted from starting the motor rapidly to its maximum speed tends to force the objects leave their original position and to harm the outer surface of the objects. On the other hand, said vibration will cause the machine to be out of order early.
According to these problems, there are numerous switches have been provided in the prior art for causing the speed of a motor increase gradually from zero to a maximum or decrease gradually from a maximum to zero. However, such switches are generally of relatively high cost which limits their use in many applications.
It therefore is a particular object of the present invention to provide a highly compact electronic switch which can be expeditiously manufactured and assembled, and which results in a switch for smoothly and effectively controlling the speed of an electric motor by degrees from low to high or from high to low as required, and thus the vibration mentioned above can be avoided.
According to this invention, a novel electronic switch comprises a stationary member, a trigger member, clip means for securing said trigger member slidably relative to said stationary member, a pair of electric cords extending from the inside of said trigger member for connecting said electronic switch in circuit with an electric motor and power source, switching means and a solid-state secomiconductor control device supported within said trigger member; said switching means comprising two sets of contacts, with one set including three electrically conductive contacts, another set including one electrically conductive contacts and a resistor for providing various resistance values, disposed on said trigger member in spaced relation to each other, and two electrically conductive bridging contacts mounted on said stationary member in isolated relation to each other for contacting with the respective set of contacts; while said trigger member being manually actuated with respect to said stationary member, the first bridging contact is movable among a non-bridging position wherein said first bridging contact engages with the first contact of the said three contacts, a first bridging position wherein said first bridging contact engages with the first and the second contacts of the said three contacts, and a second bridging position wherein said first bridging contact engages with the first and the third contacts of the said three contacts; simultaneously, the second bridging contact is movable with one end thereof slidably engaging with the contact of the associated set and the other end thereof slidably engaging with said resistor for providing various resistance values to control the application of variable magnitude of electrical energy, for varying the speed of said electric motor.
Another object of this invention is to provide an arrangement of the foregoing and other essential members which is highly compact, is economically constructed, is conveniently assemblable, and is capable of being mass produced.